As awareness of the environmental cost, and the economic cost for the disposal of organic waste has increased, individuals, companies and government authorities have a desire to use methods other than landfill when disposing of organic waste. In some countries, minimisation of organic waste to landfill is required by law.
Domestic waste in particular has a high proportion of food waste, which when processed correctly, yields both high quality liquid and solid fertiliser.
In this context, vermiculture (worm farming) has proven to be a successful means of treating organic waste streams. Generally, the worm farm comprises a container containing soil, organic matter and compost worms. Three of the most common species of worms used in vermiculture are Eisenia Foetida, Lumbricus Rubellus and Perionyx Excavatus. Organic waste is digested by the worms and ejected as castings. The castings and remaining organic matter contain high levels of nutrients and are suitable for use as fertiliser.
Conventional worm farms are generally of two types, tiered systems and continuous flow systems.
Tiered systems, such as Australian patent 737050, comprise two or more stackable trays, the lowermost a solid base with a drainage system to remove excess moisture. Additional trays are added as required and have a perforated base to allow the passage of both worms and liquids. The trays may have slightly sloping sides with the result the floor of a tray rests directly upon the organic waste contained in the tray immediately below. The trays are periodically rotated in order to remove processed waste from the lowermost tray.
Continuous flow systems, such as Australian patent 712227, comprise a single container, either elevated from the ground, or resting directly upon it. Organic waste is introduced to the top of the container and digested by the worm population within. The processed organic matter passes through container to the floor where it generally exits via a wide aperture mesh and falls onto a tray. Excess liquid is then drained from the finished castings. In some systems, the walls of the container may also be formed of a wide aperture mesh, allowing castings, liquid and worms to pass through and fall to the collection tray below.
Both systems have significant disadvantages. Tiered systems result in separate populations of worms either becoming stranded in individual trays due to a gap arising between the top of the waste present in the tray and the bottom of the tray immediately above it, or the worms failing to migrate from the lower trays to the organic waste present in higher trays because sufficient nutrients are available in the tray they are inhabiting. Worms are also able to migrate downwards to the lowest tray and drown in any liquid present. Further, due to the fact that trays must be periodically rotated, the lifecycle of the worms is disturbed. Still further, the trays when full of organic waste are a considerable weight for a single individual to lift. To overcome this problem a shallow tray may be used to enable an operator to lift its weight. However the shallow tray prevents the finished castings within from becoming compressed, allowing worms to remain active in the castings and increasing the handling weight of finished castings. In addition, trays must be entirely emptied to access the older castings situated in the bottom of the tray, and the lower tray may have substantial numbers of adult worms present which must be separated from the castings prior to use.
As stated, continuous flow systems generally rely on a wide aperture mesh to prevent the organic waste present from falling through the farm. As castings pass through the mesh and fall to a collection tray they have high moisture content and are uncompressed. The mesh in a continuous flow design can become blocked by unprocessed vegetable fibre or with the inadvertent introduction of foreign material such as plastic coated paper. Large numbers of worms and worm eggs can be present in the castings, and are unable to re-enter the farm subsequent to falling into the collection tray, reducing the overall capacity of the farm to process waste. Continuous flow designs with doors in the lower part of the farm for removal of processed waste allow removal of waste only from the side of the container in which the door is located. This results in the uneven removal of castings from within the farm.
Unless the context clearly requires otherwise, through out the description and the claims, the words ‘comprise’ and ‘comprising’, and the like are to be construed in an inclusive as opposed to an exclusive or exhaustive sense; that is to say in the sense of “including, but not limited to”.